The present invention relates to a focus detection optical system in a single lens reflex camera, and more particularly to a quick return mirror for distributing a luminous flux incident from a photographic lens system to a finder optical system and to a focus detection sensor module.
Heretofore, a focus detection sensor module has been employed in a single lens reflex camera having an auto-focus function. The single lens reflex camera is equipped with a quick return mirror which normally guides a luminous flux incident through a photographic lens system to a finder optical system except when exposure is executed.
The focus detection sensor module is usually disposed at the bottom portion of a camera, and reflects downwardly a luminous flux transmitted through the central area of a main mirror part of the quick return mirror by means of a sub-mirror part so that the luminous flux is incident upon the sensor module.
The focus detection sensor module has conventionally been constituted with fixing a visible field mask plate having light transmitting openings, a condenser lens, a mirror, an infra-red cut filter, a separator lens and a CCD (Charge Coupled Device) sensor unit onto a module main body so as to be arranged in this order from the side where light is incident. The infra-red cut filter may sometimes be interposed between the visible field mask plate and the condenser lens.
However, the above described conventional focus detection sensor module is constituted with so many number of components as to require a large number of assembling processes as well as a large occupation space.